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What is Physics? 1

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Feb 28, 2009 Merlion hit by lightning A lightning bolt struck the Merlion statue at about 4.30pm yesterday. The national icon at One Fullerton facing the Singapore River lost part of its top left mane and is believed to have its right ear chipped. About 20 to 30 people nearby, including tourists, ran helter-skelter in the pouring rain when debris from the Merlion's head went flying. Some ran to safety in the nearby shops and cafes. The fragments fell onto the patio at One Fullerton and the Singapore River Cruise counter near the Merlion. Nobody was hurt. Eyewitness Ms Rina Toh, 17, a barista at The Coffee Bean and Tea Leaf at One Fullerton, said: 'I saw a bright Z-shaped lightning bolt, and it was a lot bigger than usual.' She was standing at the counter and could see the Merlion. 3

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What is Physics? Physics is the study of the natural world around us – from the very large, such as the solar system, to the very small, such as the atom. 4

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PHYSICAL QUANTITIES, SI UNITS AND MEASUREMENT Chapter 1 In the quest to understand nature, scientists use physical quantities to describe the world around us. 5

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At the end of this chapter… You should be able to: show understanding that all physical quantities consist of a numerical magnitude and a unit recall the following base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K) use the following prefixes and their symbols to indicate decimal sub-multiples and multiples of the SI units: nano (n), micro ( μ ), milli (m), centi (c), deci (d), kilo (k), mega (M) 6

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At the end of this chapter… You should be able to: show an understanding of the orders of magnitude of the sizes of common objects ranging from a typical atom to the Earth describe how to measure a variety of lengths with appropriate accuracy by means of tapes, rules, micrometers and calipers, using a vernier scale as necessary describe how to measure a short interval of time including the period of a simple pendulum with appropriate accuracy using stopwatches or appropriate instruments 7

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Cubit 8

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Why do We Need to Measure Things? Let’s do this as a class… 1. Work in groups of two 2. Compare the length between the elbow to the first finger tip. 9

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Why do We Need to Measure Things? Are they the same? 10

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Physical Quantities and SI Units Base Quantity Name of SI unit Symbol for SI Unit Length metrem Mass kilogramkg Time seconds Electric Current ampereA Temperature kelvinK Intensity candelacd Amount of Substance molemol 11

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Physical Quantities A physical quantity when measured may be described in terms of 1. A number 2. Its unit of measurement actual length = m 12

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Physical Quantities What is your height? 2 m quantity unit 13

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Physical Quantities Mass – unit of measurement, kilogram (kg) 14

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Physical Quantities Time – unit of measurement, second (s) 15

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Physical Quantities What are some problems we might face in our daily lives if there are no standard measurements? 16

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Do You Know??? Diameter of the Sun Thickness of a strand of hair m m 0.2 mm (millimetre) 1.4 Gm (gigametre) 17

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Prefixes for SI units FactorPrefixSymbol 10 9 giga-G 10 6 mega-M 10 3 kilo-k deci-d centi-c milli-m micro-µ nano-n 18

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Prefixes Exercise 1 Express the following quantities in their respective SI unit. a. One kilometer = 1000m or 10 3 m b. One microsecond = s or s c. One centimeter= 0.01m or m d. One gram= 0.001kg or kg FactorPrefixSymbol 10 9 giga-G 10 6 mega-M 10 3 kilo-k deci-d centi-c milli-m micro-µ nano-n 19

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Prefixes Exercise 1 e. One miligram = 0.001g or g =10 -6 kg f. One millisecond= 0.001s or s g. One minute= 60s h. One hour= 3600s FactorPrefixSymbol 10 9 giga-G 10 6 mega-M 10 3 kilo-k deci-d centi-c milli-m micro-µ nano-n 20

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What does SI units mean? Système International International System of Units 21

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Measurement of Length The SI unit for length is () Other units for length: metre m millimetre (mm), centimetre (cm), kilometre (km) 22

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Measurement of Length Range Suitable Instruments Accuracy of Instruments Several metres (m) Several centimetres (cm) Between 1cm to 10cm Less than 2 cm Measuring Tape Metre/Half- metre Rule Vernier Calipers Micrometer Screw Gauge 0.1 cm (or 1 mm) 0.1 cm (or 1 mm) 0.01 cm (or 0.1 mm) cm (or 0.01 mm) 23

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Measurement of Length Measuring Tape - Length of classroom, car, corridor Metre rule: Length of desk, book 24

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Measurement of Length Parallax Error What is Parallax Error? It is the error which arises due to incorrect positioning of the eye. 3.0 cm wrong 2.7 cm correct cm

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Measurement of Length Parallax Error How do we avoid Parallax Error? Always place the eye vertically above the mark being read.OR Place the eye in level with the mark being read. 3.0 cm wrong 2.7 cm correct cm

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Vernier Calipers French scientist Pierre Vernier( ) Accuracy: 0.01 cm (or 0.1 mm) 27

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How to read off the Vernier Caliper? mm Measured Value 11mm0.7mm Reading = 11 mm mm = 11.7 mm 28

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Its structure and its application Vernier Calipers Its structure and its application The inside jaws is used to measure internal diameter of test-tube, ring etc. In main scale, reading = 1.90 cm in vernier scale, reading = 0.01 cm the actual reading = 1.91 cm 29

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Its structure and its application Vernier Calipers Its structure and its application The outside jaws is used to measure small length, diameter of test-tube etc. main scale reading = 4.20 cm vernier scale reading = 0.06 cm Actual reading = 4.26 cm 30

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Exercise 1 Reading = 19 mm mm = 19.4 mm mm 31

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Exercise 2 mm Reading = 4 mm mm = 4.7 mm 32

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Exercise 3 33

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Exercise 4 34

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Exercise 5 mm Reading = 12 mm mm = 12.6 mm 35

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Exercise 6 mm Reading = 7 mm mm = 7.5 mm 36

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Vernier Calipers Zero Error (Vernier Calipers) Positive Zero Error Zero Error = mm If the observed reading = 32.4mm, then Actual measurement = Observed reading – Zero error = mm = cm (+0.1) main scale (fixed) vernier scale (movable) mm +0.1 mm 38

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Vernier Calipers Zero Error (Vernier Calipers) Negative Zero Error Zero Error = mm If the observed reading = 32.4 mm, then Actual measurement = Observed reading – Zero error = mm (-0.2) main scale (fixed) vernier scale (movable) mm mm 39

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Micrometer Screw Gauge Accuracy: cm (or 0.01 mm) Smaller length, such as diameter of thin wire, thickness of a piece of paper etc can be measured by micrometer screw gauge. 40

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Micrometer Screw Gauge Sleeve reading =mm Thimble reading= mm Reading = mm Reading = cm 3 mm 0.09 mm

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Micrometer Screw Gauge Sleeve reading =mm Thimble reading= mm Reading = mm Reading = cm 5.5 mm 0.30 mm

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Micrometer Screw Gauge Sleeve reading =mm Thimble reading= mm Reading = mm Reading = cm 3.5 mm 0.06 mm

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Exercise mm0.25mm Reading = 11.5 mm mm = mm 44

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Exercise Reading = 20.5 mm mm = mm 45

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Micrometer Screw Gauge Zero Error (Micrometer Screw Gauge) Positive Zero Error Zero Error = mm If the observed reading = 2.37mm, then Actual measurement = Observed reading – Zero error = mm (+0.02) mm 46

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Micrometer Screw Gauge Zero Error (Micrometer Screw Gauge) Negative Zero Error Zero Error = mm If the observed reading = 2.37mm, then Actual measurement = Observed reading – Zero error = mm (- 0.03) mm 47

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Measurement of Time Stopwatches are used to measure short intervals of time. Two types: Digital stopwatch Analogue stopwatch SI unit of time: second, s 48

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Measurement of Time InstrumentsUsage Accuracy of Instruments Watch/Clockhrs, mins, sec Analogue Stopwatch mins, sec Digital Stopwatch mins, sec Atomic Clockabout s- Pendulum Clockhrs, mins, sec- Radioactive decay clock thousand of years - 1 s 0.1 s 0.01 s 49

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Measurement of Time Watch/Clock used for measuring long intervals of time most modern watches depend on the vibration of quartz crystals to keep time accurately the energy that keeps these crystals vibrating comes from a small battery many watches still make use of coiled springs to supply the needed energy used for measuring long intervals of time most modern watches depend on the vibration of quartz crystals to keep time accurately the energy that keeps these crystals vibrating comes from a small battery many watches still make use of coiled springs to supply the needed energy 50

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Measurement of Time Stopwatch (Analogue/Digital) Analogue Stopwatch accuracy = 0.1 s Digital Stopwatch accuracy = 0.01 s 51

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Measurement of Time Atomic Clock 52

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Measurement of Time Pendulum Clock 53

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What is a pendulum? A small object suspended by a piece of string or tread is called a simple pendulum. The distance from the centre of the pendulum bob to the point of suspension is called the length of the pendulum. One complete to and fro movement of the pendulum is called an oscillation. The time taken for one complete oscillation is called the period. The distance between the rest position of the pendulum and the extreme point of its oscillation is called the amplitude. 54

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Diagram of a Pendulum B A C Oscillation From A to B to C and back to B to A Amplitude From B to C Length of Pendulum 55

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Finding the Period of a Pendulum To find the period: 1. Take the total time for 20 oscillations. Why 20? 2. Repeat 2 more times. 3. Calculate the average time for 20 oscillations. 4. Divide by 20 to obtain the period. 57

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What Affects the Period of a Pendulum? Mass? Amplitude? Length? 58

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Simple Pendulum When the length increases, the period increases. When the length decreases, the period decreases. When the mass of the bob increases/decreases, there is no effect on the period. 59

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When the amplitude of the bob increases/decreases, there is no effect on the period. When the same experiment is done on the moon, the period increases. Simple Pendulum 60

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Pendulum Exercise The time taken for a pendulum to swing from rest position A to B is 0.8s. What is the time taken for the pendulum to make 20 oscillations? 61

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